The fat-derived hormone leptin acts on neurons in the hypothalamus to regulate food intake and body weight in rodents and humans. The aim of this proposal is to identify and characterize a novel signaling mechanism whereby leptin affects neuronal activity of POMC and AgRP neurons. Specifically, we will test the hypothesis that leptin receptors localized on dendrites of POMC and AGRP neurons regulates phosphorylation and activity of post-synaptic glutamate receptors (NMDA-R(NR1/NR2B)), and that this pathway influences dendrite morphology, and eventually plays a role in energy balance regulation in mice. To achieve this, we will investigate leptin receptor signaling and action in cell lines, primary neuronal cultures, brain slices and in vivo in mice. We will use state- of-the art methodologies and create/use novel genetically modified mice, and study leptin's effects on neuronal plasticity and on energy balance in mice lacking specific NMDA receptor subunits in POMC or AgRP neurons. Findings from this proposal will lead to a significant advancement in our understanding of leptin receptor neurobiology. We will elucidate a new CNS pathway whereby leptin regulates energy balance.